The invention relates to a device for variably adjusting the timing of gas exchange valves of an internal combustion engine having a hydraulic phase adjustment unit and at least one volume accumulator, wherein the phase adjustment unit can be brought into drive connection with a crankshaft and a camshaft and at least one advance chamber and at least one retardation chamber, which can be supplied with pressure medium or from which pressure medium can be discharged via pressure medium lines, wherein a phase position of the camshaft relative to the crankshaft can be adjusted in the direction of early timing by supplying pressure medium to the advance chamber while simultaneously allowing pressure medium to flow out of the retardation chamber, wherein a phase position of the camshaft relative to the crankshaft can be adjusted in the direction of late timing by supplying pressure medium to the retardation chamber while simultaneously allowing pressure medium to flow out of the advance chamber, wherein pressure medium can be supplied to the volume accumulator or accumulators during the operation of the internal combustion engine.
In modern internal combustion engines, devices for variably adjusting the timing of gas exchange valves are used to enable variable configuration of the phase position of a camshaft relative to a crankshaft within a defined angular range between a maximum advance position and a maximum retardation position. For this purpose, a hydraulic phase adjustment unit of the device is integrated into a drive train via which torque is transmitted from the crankshaft to the camshaft. This drive train can be implemented as a belt, chain or gear drive, for example. The phase adjustment speed and the pressure medium requirement are significant parameters of such devices. To enable the phase position to be adapted in an optimum manner to the various driving situations, high phase adjustment speeds are desirable. In the context of measures for reducing consumption, there is furthermore a demand for an ever smaller pressure medium requirement so as to enable the pressure medium pump of the internal combustion engine to be of smaller design or to enable the delivery rate to be reduced when using controlled pressure medium pumps.
A device of this kind is known from EP 0 806 550 A1, for example. The device comprises a phase adjustment unit of the vane cell type with a drive input element, which is in drive connection with the crankshaft, and a drive output element, which is connected to the camshaft for conjoint rotation therewith. A plurality of pressure spaces is formed within the phase adjustment unit, wherein each of the pressure spaces is divided into two pressure chambers with an opposed action by means of a vane. The vanes are moved within the pressure spaces by supplying pressure medium to or discharging pressure medium from the pressure chambers, thereby bringing about a change in the phase position between the drive output element and the drive input element. In this case, the pressure medium required for phase adjustment is made available by a pressure medium pump of the internal combustion engine and is directed selectively to the advance or retardation chambers by means of a control valve. The pressure medium flowing out of the phase adjustment unit is directed into a pressure medium reservoir, the oil sump of the internal combustion engine. Phase adjustment is thus accomplished by means of the system pressure made available by the pressure medium pump of the internal combustion engine.
Another device is known from U.S. Pat. No. 5,107,804 A, for example. In this embodiment, the phase adjustment unit is likewise of the vane cell type, and a plurality of advance and retardation chambers is provided. In contrast to EP 0 806 550 A1, phase adjustment is not accomplished by supplying pressure medium to the pressure chambers by means of a pressure medium pump; instead, alternating moments acting on the camshaft are used. The alternating moments are caused by the rolling movements of the cams on the gas exchange valves, each of which is preloaded by a valve spring. In this case, the rotary motion of the camshaft is braked during the opening of the gas exchange valves and accelerated during closure. These alternating moments are transmitted to the phase adjustment unit, with the result that the vanes are periodically subjected to a force in the direction of the retardation stop and of the advance stop. As a result, pressure peaks are produced alternately in the advance chambers and the retardation chambers. If the phase position is supposed to be held constant, pressure medium is prevented from flowing out of the pressure chambers. In the case of a phase adjustment in the direction of earlier timing, pressure medium is prevented from flowing out of the advance chambers, even at times at which pressure peaks are being produced in the advance chambers. If the pressure in the advance chambers rises owing to the alternating moments, this pressure is used to direct pressure medium out of the retardation chambers into the advance chambers, using the pressure of the pressure peak generated. Phase adjustment in the direction of later timing is accomplished in a similar way. In addition, the pressure chambers are connected to a pressure medium pump, although only to compensate for leaks from the phase adjustment unit. Phase adjustment is thus accomplished by diverting pressure medium out of the pressure chambers to be emptied into the pressure chambers to be filled, using the pressure of the pressure peak generated.
Another device is known from US 2009/0133652 A1. In this embodiment, phase adjustment at small alternating moments is accomplished, in a manner similar to the device in EP 0 806 550 A1, by supplying pressure to the advance chambers or the retardation chambers by means of a pressure medium pump while simultaneously allowing pressure medium to flow out of the other pressure chambers to the oil sump of the internal combustion engine. In the case of high alternating moments, as in the device in U.S. Pat. No. 5,107,804 A, these are used to direct the pressure medium under high pressure out of the advance chambers (retardation chambers) into the retardation chambers (advance chambers). During this process, the pressure medium expelled from the pressure chambers is fed back to a control valve, which controls the supply of pressure medium to or discharge of pressure medium from the pressure chambers. This pressure medium passes via check valves within the control valve to the inlet port, which is connected to the pressure medium pump, wherein some of the pressure medium is expelled into the pressure medium reservoir of the internal combustion engine.